The development of a non-human primate animal model for subacute sclerosing panencephalitis (SSPE) is in progress. It appears that clinical signs of encephalitis can be produced in immunosuppressed cynomolgus monkeys inoculated with a defective strain of SSPE virus. However, the course of the disease when clinical signs are first seen is so acute that the animals die before the typical symptoms of SSPE can develop. Animals are now on test that have not been immunosuppressed and should not have such an acute course of encephalitis.